Preparation of Fe/Fe₃O₄/N-doped kapok-based carbon fibers and their microwave absorption performance

With the rapid advancement of electronic information technology, the threat posed by radar detection has intensified. Consequently, developing electromagnetic wave-absorbing materials that are highly efficient, lightweight, and broadband has become a key research direction in materials science. In this study, natural hollow kapok fibers served as carbon precursors to fabricate Fe/Fe₃O₄/N-doped kapok-based carbon fiber composites (CKF@Fe/Fe₃O₄/N). An in-situ growth method was employed to uniformly load iron and nitrogen elements (KF@Fe/N) on both the inner and outer fiber surfaces, followed by high-temperature carbonization. This study thoroughly investigated how Fe/N co-doping regulates the electromagnetic parameters of kapok carbon fibers and elucidated the influence of carbonization temperature on microwave absorption performance. The results indicate that Fe/N co-doping introduces abundant heterogeneous interfaces, dipole polarization centers, and magnetic loss mechanisms into the carbon fiber matrix while preserving the unique hollow tubular structure of kapok fibers. At a carbonization temperature of 800 ℃ and the mass fraction of the microwave absorber is 9%, the CKF@Fe/Fe₃O₄/N composite exhibits optimal microwave absorption performance: a minimum reflection loss of −35.7 dB at a thickness of 4 mm and a frequency of 9.0 GHz, and a maximum effective absorption bandwidth of 7.2 GHz at a thickness of 3.5 mm, covering the dual bands of 8.3-10.3 GHz and 10.5-15.7 GHz. This study provides a new strategy for designing lightweight, high-efficiency microwave-absorbing materials using biomass-derived hollow structures.